Thanks, you are as always very helpful. I hope I'll be able to compose a PR
soon.
On Thursday, July 23, 2015 at 5:39:52 PM UTC+3, Michael Bayer wrote:
>
>
>
> On 7/23/15 10:09 AM, Mike Bayer wrote:
>
>
>
> On 7/23/15 1:24 AM, Yegor Roganov wrote:
>
> Hi all!
> Is there a way to disable implicit loading of relationships?
> For example, I want an exception to be thrown if I try to access
> 'address.user' unless user was explicitly loaded via options
>
> address =
>> query(Address).options(joinedload(Address.user)).filter_by(id=id).first();
>> address.user # OK
>> address = query(Address).get(id); address.user # should throw
>
>
> At first I thought that `noload` option is what I need, but it seems it
> disables event explicit loading.
>
> noload is how you'd disable implicit loading. As far as throwing on a
> lazyload, the easiest way is just to detach the objects from their parent
> Session so they no longer have any connectivity using
> session.expunge(object), but then you're no longer in the session.
>
> Otherwise, it seems the problem you are actually trying to solve is
> raising on unexpected SQL. lazy loading of relationships is not the only
> thing that goes on, there are loads of unloaded columns, columns that had
> server defaults emitted on the last flush, loads of joined-inheritance
> rows, all kinds. this is why the best approach is to just do real
> profiling of your applications using SQL logging, or perhaps using SQL
> events like before_execute() / before_cursor_execute() so that you can
> build yourself a "with assert_no_sql(session):" -style context manager for
> critical blocks that should have no SQL emitted.
>
>
> Guessing that's not what you want. Feel free to write your own
> NoLoader that just raises, example:
>
>
> whoops. Let's try that again, this one actually works:
>
> from sqlalchemy.orm import properties
> from sqlalchemy.orm import strategies
> from sqlalchemy.orm import state
>
>
> @properties.RelationshipProperty.strategy_for(lazy="raise")
> class RaiseLoader(strategies.NoLoader):
> """note: this is *very SQLAlchemy 1.0 specific*!!
> it will need to be reviewed for 1.1"""
>
> def create_row_processor(
> self, context, path, loadopt, mapper,
> result, adapter, populators):
>
> def invoke_no_load(state, passive):
> raise Exception("boom")
> set_lazy_callable = state.InstanceState.\
> _instance_level_callable_processor(
> mapper.class_manager,
> invoke_no_load,
> self.key
> )
> populators["new"].append((self.key, set_lazy_callable))
>
>
>
>
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